The HII region NGC 281 (also known as Sharpless
184) is a classic star forming complex consisting of an ionization
front formed on the edge of a molecular cloud, and illuminated
by its progeny of young stars. The complex is located in the Perseus
arm of our galaxy and its visible structure spans some 60 light
years. The molecular cloud counterpart has been busy in the last
few million years forming the massive young stars of the central
cluster IC 1590. IC 1590 is the source of ionization for the visible
nebula and an excellent example of a very young cluster where
pre-main sequence stars can be found in abundance, indicating
active and ongoing star formation.

The visible nebula contains a variety of
elephant trunk-like pillars and dark globules and a conspicuous
incursion of foreground dust into the southwestern quadrant of
the visible nebula. NGC 281 is a relatively bright HII region
which formed between one and two million years ago as a thin ionization
front on the edge of an extensive molecular cloud complex. The
molecular cloud complex has been mapped using the tracer CO (carbon
monoxide) and has been found to have two distinct components,
a southeastern component N281A associated with the visible nebula,
and a southwestern component N281B. The southwestern component
of the molecular cloud is foreground to our line of site and forms
the dusty incursion into the southwest region of the nebula. Within
the southwestern cloud convincing signs of active star formation
have been identified. Bipolar outflows of hot gas ejected from
infant protostars and a radio source identified as a "water
vapor maser" are convincing evidence of ongoing star formation
in the southwestern cloud. The formation of water masers requires
a high energy source to form molecules of water from the ambient
gases in the cold cloud. The energetic outflows of protostars
provide this source which explains why water masers are found
in areas of active starbirth.

IC 1590 is a fascinating young cluster with
a central core of OB stars within its center known as ADS 719
(Aitken 1932). The core is a trapezium-like system of closely
spaced O and B type stars confined to a small region of about
8000 AU (astronomical units). The brightest star of the system
is the O5.5 giant HD 5005. This star is the dominant ionization
energy source for the surrounding HII region. Compact groupings
of bright O and B type stars tend to form at the center of open
clusters. Known as "trapezium systems" (named after
the prototypical trapezium cluster of the Orion Nebula) they were
once thought to be unstable because of their narrow separation
distances. They are now known to be long lived stable stellar
systems that exist in several well known clusters. The formation
of the stars of IC 1590 began some 3.5 million years ago and likely
continues today in the southwest quadrant of the complex.

Several compact globules known as Bok globules
are projected against the background of the emission nebula. These
compact dark structures were first described by the astronomer
Bart Bok (1906-1983) in the 1940's. Bok Globules are small dark
clouds of gas and dust that are found in HII regions and typically
have a mass of about 10 to 50 solar masses. They often span a
region of about one light year across. Their contents are predominantly
molecular hydrogen, carbon oxides and helium but also contain
about 1% silicate dust. Infrared observations in the 1990's detected
the existence of protostars within the dense confines of Bok globules
confirming the hypothesis of Bok, who strongly believed that these
globules represented cocoons of starbirth. The larger Bok globule
seen in the image is about 2.6 light years in diameter.